Coating of particulate solids or powdered materials in a fluidized bed has been used for many years, particularly in the pharmaceutical industry, however, other industries have utilized this general process including powder metallurgy, ceramics, chemical processing, cosmetics, food and agriculture industries. Relatively little has been published regarding the basic fundamentals of such processes. Thus, during the manufacturing of powdered materials some surface treatment is often desired. For example, the application of a pigment or protective coating may be beneficial. One example of a coating treatment is taught in U.S. Pat. No. 4,710,674, which describes the deposition of a conformal protective coating of Al.sub.2 O.sub.3 on phosphor particles via a fluid bed-chemical vapor deposition process.
Phosphor particles are usually in the particle size range of from about 3 micrometers to about 20 micrometers and in their untreated state exhibit significant interparticle cohesive forces. Powders such as phosphors are not free flowing and tend to cake and do not fluidize well in a fluid bed operation. Heretofore, lubricants have been added to powders at a fixed level to obtain fluidity, however, it has been discovered that results are sometimes erratic and unpredictable.
It is believed, therefore, that a process for applying a lubricant to a powdered material whereby uniform and operational levels of controlled fluidity are achieved accompanied by relative uniform and desired bulk density characteristics is an advancement in the art.